This invention relates to apparatus for calcining of particulate materials, and more particularly to calcining of material such as petroleum coke in vertical shaft kilns.
Petroleum coke is conventionally calcined at high temperature to drive off volatile materials and moisture, and to alter the coke properties so that it may be made into useful products. Most commercial calciners are of the inclined rotary kiln type, but there are advantages in using a vertical shaft kiln for this purpose. A thorough description of a vertical shaft kiln and its operation is found in U.S. Pat. No. 4,251,323.
One petroleum encountered in operating an internally-fired large diameter vertical shaft kiln is obtaining good distribution of injected combustion air. Injection of air through holes in the kiln wall does not provide sufficient air to the central part of the kiln.
The prior art relating to gas injection in shaft kilns, in addition to the above-mentioned U.S. Pat. No. 4,251,323, includes U.S. Pat. No. 2,933,297, which describes horizontal water-cooled gas inlets extending across the interior of the kiln. These horizontal distributors, however, interfere with the downwardly flowing bed of particulate material, and in cases where very high temperatures are required, such as in calcining and desulfurizing petroleum coke at from 1300.degree. to 1600.degree. C., the heat losses from air distributors of the type shown in U.S. Pat. No. 2,933,297 are excessive, and the metal in the distributors is subject to getting too hot to maintain structural integrity.
Thus, a need exists for an air injection system capable of injecting combustion air uniformly throughout the cross section of a vertical shaft kiln and capable of withstanding the severe temperatures encountered in calcining and desulfurizing petroleum coke. Such a system is provided by the present invention.